JP2879342B2 - Electron beam excited ion source - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electron beam-excited ion source that generates ions by an electron beam, extracts the generated ions, and emits the ions, and in particular, has a low energy and a large current. The present invention relates to an electron beam excited ion source capable of generating an ion beam.

(Prior Art) The present applicant has already proposed an electron beam ion source capable of generating a low-energy, high-current ion beam without the limitation of space charge generated near an accelerating cathode for accelerating electrons. (Japanese Patent Application No. 60-132138). In this ion source, a plasma region, an acceleration cathode, an electron beam acceleration region, an acceleration anode, an ion generation region, and a target cathode are provided in this order, and a negative potential is applied to the target cathode with respect to the acceleration anode. Means and an ion extraction electrode for absorbing positive ions or negative ions generated in the ion generation region and extracting the ions. When the ion source is configured in this manner, electrons in the plasma region are extracted by the accelerating anode and enter the ion generation region. The rushed electrons collide with the inert gas (or metal vapor) in the ion generation region to generate ions. The backflow of the ions neutralizes the negative potential barrier formed near the exit of the accelerating cathode. You. Therefore, a large current electron beam proportional to the plasma density flows into the ion generation region. In the ion generation region, a plasma containing a number of ions proportional to the current value of the flowing electron beam is generated, and the ions in the generated plasma are attracted by the ion extraction electrode and radiated out of the ion generation region. .

The applicant of the present application has previously proposed an electron beam excitation ion source capable of further simplifying, miniaturizing, and reducing the cost of such an ion source (Japanese Patent Application No. 61-121967).
issue).

(Problems to be Solved by the Invention) Even in the ion source as described above, in order to extract monoatomic ions with high efficiency using a material gas composed of polyatomic molecules, more sufficient dissociation and ionization of molecules are required. Required.

(Means for Solving the Problems) The above-mentioned problem is solved by providing a magnetic field generating means for generating a magnetic field in a direction intersecting discharge between the cathode and the anode.

(Operation) In the present invention, since a magnetic field is applied between the cathode and the anode in a direction crossing the discharge, the discharge in this region is a PIG (Philips Ionization Gauge) discharge, and the dissociation of gas molecules introduced therein is performed. -Excitation can be performed strongly.

That is, in the present invention, the space between the cathode and the anode not only functions as an electron source for generating an electron beam, but also dissociates polyatomic molecules such as BF ₃ and neutralizes B and the like. Used to generate a single atom. Neutral mon atoms produced by the dissociation of polyatomic molecules diffuse out or follow the flow of gas out of between the anode and cathode, where they are excited (collision) by a strong electron beam,
A positive ion atom such as B ⁺ is generated. In this way, monoatomic ions can be efficiently extracted.

(Effect of the Invention) According to the present invention, the material gas, which was insufficiently decomposed by the conventional electron beam ion source, is efficiently dissociated by the PIG discharge. Can be greatly increased. Also, in the present invention, since the electron source for generating the electron beam is not a thermionic source, it is possible to stably generate high-current monoatomic ions from a wide range of polyatomic molecular gas species including highly reactive gases for a long time. become.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In each embodiment, the same components will be described with the same reference numerals.

FIG. 1 is a schematic diagram of a preferred embodiment of the present invention.
The cathode 1, which is one electrode for performing discharge, is formed of a material such as tantalum and has a cylindrical shape. The cathode 1 has a through hole 1 'through which a discharge gas, for example, argon gas, flows into the apparatus. An anode 2 is provided to face the cylindrical cathode 1. The anode 2 is a conductor provided with a slit or a cylindrical through-hole. A discharge voltage is applied between the cylindrical cathode 1 and the porous anode 2 by a discharge power source 3 to generate plasma by glow discharge. This discharge voltage may be a low voltage such as 500 V, for example. Between the cylindrical cathode 1 and the porous anode 2, there are provided two divided microconductance bottlenecks 4, 4 '. The magnitude of the conductance of the bottlenecks 4 and 4 'is, for example, 0.3- gas pressure in the chamber on the cathode 1 side.
The gas pressure in the chamber on the side of the anode 2 is selected to be kept at 1.0 Torr, preferably 0.8 Torr, and 0.01-0.04 Torr. The bottleneck 4 also serves as an intermediate electrode. Most of the inner surface of the hole of the bottleneck 4 on the anode side is covered with an insulator 5, for example, an alumina-based ceramic,
The discharge between the cathode 1 and the anode 2 is made easy. The bottleneck 4 'is made of an insulating material, and the bottleneck 4,
A gas inlet 12 for introducing a material gas is provided between 4 '. A magnetic field B is applied between the cathode 1 and the anode 2 in a direction crossing a discharge (electric field E). This magnetic field B is formed by the poles 11, 11 'having opposite polarities,
It is generated locally at the portion 4 '. The magnetic field may be generated by a permanent magnet or an electromagnet. By applying a magnetic field in the direction that intersects the discharge in this way, a PIG discharge occurs,
Neutral monoatomic molecules (eg, B) are efficiently produced from polyatomic molecules (eg, BF ₃ ).

An electron beam acceleration electrode 6 and ion extraction electrodes 7 and 7 'are provided below the anode 2. There is a gap of 0.5-1.5 mm between the anode 2 and the electron beam accelerating electrode 6, an accelerating voltage is applied between these electrodes by the power source 8, and the cathode 1 and the anode Electrons are extracted from the plasma generated by the discharge between the two,
Further, it functions as an electron beam acceleration region for accelerating the electrons. An ion extraction voltage is applied between the electron beam acceleration electrode 6 and the ion extraction electrodes 7, 7 'by power supplies 9, 9', respectively. Between the electron beam accelerating electrode 6 and the ion extraction electrodes 7 and 7 ', the accelerated electrons collide with neutral monoatomic molecules (for example, B) to produce ions (for example, B ⁺ ).
And electrons are generated, and the ions function as an ion generation region in which ions are accelerated.

A vacuum exhaust port 10 for exhausting gas in the apparatus is provided only downstream of the ion extraction electrodes 7, 7 '. This exhaust port 10
When the pressure in the apparatus is reduced through the above, the amount of exhaust is selected so that the bottlenecks 4, 4 'and each part blocked by each electrode have the desired vacuum value. 0.8 Torr between cathode 1 and bottlenecks 4 and 4 'when bottles were actually exhausted, bottlenecks 4 and 4'
0.1 Torr between the anode and the anode 2;
The distance between the electrode and the ion extraction electrode 7 could be set to a desired value of 0.01 Torr.

In operation, the material gas is supplied from the gas inlet 12 while the gas is exhausted from the exhaust port 10 and the operation is performed. First, a discharge is generated between the cathode 1 and the anode 2, and thereafter, a bottleneck 4,
4 ', a local magnetic field of, for example, about 100 to 150 Gauss is applied. The material gas is strongly dissociated in the discharge plasma in the magnetic field application region. Since the discharge occurs through the bottlenecks 4, 4 'and is maintained in a direction crossing the magnetic field, the density of the plasma and the electron temperature are relatively high. Therefore, polyatomic molecules, performed easily e.g. dissociation of BF ₃ is able to significantly increase the proportion of single atoms B in the gas. Therefore, it is possible to extract a large-current monoatomic ion.

Next, an embodiment in which the ion source of the present invention is applied to an ion source for an ion implantation apparatus will be described with reference to FIG.

At one end of the cylindrical airtight container, a cathode 1 serving also as a supply pipe for a glow discharge gas is provided. This cathode 1
Bottlenecks 4, 4 'are provided to maintain the gas pressure in the side chamber at, for example, 0.8 Torr. Discharge is performed between the cylindrical cathode 1 and the porous anode 2 by a discharge power supply 3 to generate plasma. An auxiliary discharge anode 13 is provided between the bottlenecks 4 and 4 '. As the auxiliary discharge anode, for example, a ring of a conductive plate having an inner diameter of 4 cm can be used. This device also has an auxiliary discharge anode 13
Is provided with a solenoid coil 14 including the solenoid coil. This coil 14 allows for example 10
An external magnetic field B of about 0-150 Gauss is applied. Material gas is introduced from the gas inlet 12. An auxiliary discharge (electric field E) is maintained between the cathode 1 and the auxiliary discharge anode 13 by another discharge power supply 15. Since this auxiliary discharge (electric field E) is a discharge that crosses the magnetic field B (so-called PIG discharge), the electron temperature is high, and the material gas introduced therein is efficiently dissociated. The monoatomic molecules generated by the dissociation flow into the ion generation region 16 and are further ionized by the electron beam to form high-density plasma, thereby generating monoatomic ions. Bottleneck 4
Most of the inner surface of the hole of the auxiliary discharge anode side and the end surface of the auxiliary discharge anode side are covered with an insulator 5, for example, alumina-based ceramic. Is easily discharged. Bottleneck 4 'is made of insulating material,
The through hole may have, for example, a slit shape for forming a plasma that matches the shape of the through hole of the ion extraction electrode.

An electron beam accelerating electrode 6 is provided below the anode 2. An interval between the anode 2 and the electron beam accelerating electrode 6 is 0.5 to 1.5 mm, and an accelerating voltage is applied by the power supply 8. Between the electrodes 2 and 6, electrons are extracted from plasma generated by the discharge between the cathode 1 and the anode 2 and further function as an electron beam acceleration region for accelerating the electrons. Further, between the electron beam accelerating electrode 6 and the ion extraction electrodes 7, 7 'of the ion deriving section 17, the accelerated electrons collide with the neutral gas to generate plasma. The ions for ion implantation are extracted in the ion deriving unit 17 from the plasma thus generated. The shapes of the ion electrodes 7, 7 'of the ion deriving section 17 can be square and elliptical, respectively. The configuration of this slit is the electrode configuration of the ion deriving unit 17 used in the ion source of the well-known ion implantation apparatus. Specifically, the slit of the electrode 7 is a vertically long rectangular through hole of 1.5 mm × 20 mm. , The slit of the electrode 7 'should be 5mm long and 2mm long
A 0 mm elliptical through hole can be used. The ion beam passing through these electrodes 7 and 7 'is emitted into a magnetic field for mass analysis of the ion implantation apparatus.

FIG. 3 shows another embodiment of the present invention. this is,
FIG. 2 shows an example in which an external magnetic field B is applied using a permanent magnet 18 in the embodiment of FIG. Magnetic lines of force are iron yokes 19, 19 '
And is collected only near the auxiliary discharge anode 13.

FIGS. 4 and 5 show still another embodiment of the present invention. These are examples of ion sources that extract and accelerate ions in a direction perpendicular to the direction of the initial discharge, and the surface of the anode 2 is installed parallel to the axis of the cylindrical cathode 1. In the embodiment shown in FIG. 4, the magnetic field B generated by passing a current through the coil 20 is concentrated only on the PIG discharge portion by the iron yoke 21. In the embodiment shown in FIG. 5, a magnetic field B is applied near the central axis of the ion source by the yoke pole tips 22, 22 'sandwiching the entire apparatus from the outside. In the embodiment shown in FIGS. 4 and 5, the power supply for the auxiliary discharge anode 13 is shared with the power supply 3 for the anode 2. If the PIG discharge is sufficiently performed by the anode 2, the auxiliary discharge anode 13 is not always necessary. Furthermore, it should be noted in the examples shown in FIGS. 4 and 5 that the electron acceleration region is located outside the applied magnetic field. If a strong external magnetic field is applied to this region, it becomes difficult to accelerate electrons without loss.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view of a preferred embodiment of an electron beam excited ion source according to the present invention, and FIG. 2 is a schematic side sectional view of an embodiment when the present invention is applied to an ion source for an ion implantation apparatus. 3 to 5 are schematic side sectional views showing the configuration of still another embodiment of the present invention. (Explanation of reference numerals) 1 ... Cathode, 1 '... Cathode through-hole, 2 ... Anode, 3 ... Discharge power supply, 4,4' ... Bottle, 5 ... Insulator, 6 ... Electron beam acceleration Electrode, 7, 7 '... Extraction electrode, 8 ... Power supply, 9, 9' ... Power supply, 10 ... Vacuum exhaust port, 12 ... Material gas inlet, 13 ... Anode for auxiliary discharge, 14 ... Solenoid coil, 15… Discharge power supply, 16 ……
Ion generation area, 17 ... Ion derivation section, 18 ... Permanent magnet, 19,19 '... Iron yoke, 20 ... Coil, 21 ... Iron yoke, 22,22' ... Magnetic pole tip.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Susumu Namba 2-1 Hirosawa, Wako-shi, Saitama Pref. RIKEN (56) References JP-A-62-278736 (JP, A) JP-A-60-240039 (JP) JP-A-63-81735 (JP, A) JP-A-1-176633 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01J 27/00-27/ ²⁶ H01J 37/08

Claims (8)

(57) [Claims] An electric discharge is generated between a cathode and an anode,
An electron beam excited ion source that generates ions by exciting an electron beam generated by being extracted from between the cathode and the anode, and extracts and radiates the generated ions, between the cathode and the anode. A raw material gas inlet is provided, for the purpose of dissociating the raw material molecules,
An electron beam excited ion source, comprising: a magnetic field generating means for generating a magnetic field in a direction intersecting a discharge between the cathode and the anode. 2. The electron beam excited ion source according to claim 1, wherein the discharge generated in a direction intersecting the magnetic field is generated between the cathode and the anode. 3. The electron beam according to claim 2, wherein the cathode has a cylindrical shape, and the surface of the anode is installed in parallel with the axis of the cathode. Excitation ion source. 4. A yoke having a gap with the anode and being opposed to the anode so as to generate a magnetic field in parallel with the anode, and a magnetic pole having an opposite polarity at a tip of the yoke. The electron beam excited ion source according to claim 3, wherein the ion beam excitation ion source comprises a magnet. 5. A magnetic field generating means for generating a magnetic field having a gap with the anode and opposed to the anode so as to generate a magnetic field in parallel with the anode, and a magnetic pole having an opposite polarity at a tip of the yoke. The ion beam excitation ion source according to claim 3, wherein the ion beam excitation ion source comprises an air-core coil. 6. A discharge generated in a direction intersecting with the magnetic field is generated between an auxiliary discharge anode provided between the cathode and the anode and the cathode. Item (1). 7. The electron beam excited ion source according to claim 6, wherein said magnetic field generating means is an air-core coil provided between said cathode and said anode. 8. The magnetic field generating means comprises a yoke opposed to the cathode and the anode with a gap therebetween, and a magnet for generating a magnetic pole of opposite polarity at the tip of the yoke. An electron beam excited ion source according to claim 6.